Muffler

ABSTRACT

Provided is a muffler having a double pipe portion formed therein in which an end portion of a first tubular member is inserted into a second tubular member from an end portion thereof. A leading end portion of the second tubular member is joined to an outer periphery of the first tubular member. A portion that forms the double pipe portion of the second tubular member comprises a first portion located closer to an end of the first tubular member, and a second portion that is located closer to an end of the second tubular member and that has an enlarged diameter compared with the first portion. A resonance chamber is formed between the first tubular member and the second portion. A communication path that allows communication between an exhaust flow path and the resonance chamber is formed between the first tubular member and the first portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This international application claims the benefit of Japanese PatentApplication No. 2013-003714 filed Jan. 11, 2013 in the Japan PatentOffice, and the entire disclosure of Japanese Patent Application No.2013-003714 is incorporated herein.

TECHNICAL FIELD

The present invention relates to a muffler that reduces exhaust noise.

BACKGROUND ART

In an exhaust system for an automobile, exhaust noise is reduced by amuffler provided in an exhaust flow path. For example, low-frequency aircolumn resonance generated in a tubular portion having a long actuallength is a factor that increases muffled exhaust noise. Thus, measuresare taken, such as reducing the air column resonance by providing asub-muffler in series with a main muffler. Moreover, Patent Document 1includes a structure in which a muffler of a side branch type resonantsystem is provided between the main muffler and the sub-muffler.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Unexamined Patent Application    Publication No. 2005-105918

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

As a muffler of a resonant system, a muffler of a Helmholtz typeresonant system is known in addition to the above-described muffler ofthe side branch type resonant system. However, the Helmholtz typemuffler is formed with a structure in which the exhaust flow path leadsto a resonance chamber having a large volume via a long and narrowcommunication path, and thus, a problem has been found in which thestructure is inevitably complicated.

In one aspect of the present invention, it is preferable to form amuffler of a Helmholtz type resonant system with a simple structure.

Means for Solving the Problems

An aspect of the present invention is a muffler that comprises a firsttubular member that forms an exhaust flow path of an internal combustionengine, and a second tubular member that is connected to the firsttubular member and forms the exhaust flow path together with the firsttubular member. A double pipe portion is formed in which an end portionof the first tubular member is inserted into the second tubular memberfrom an end portion thereof. A leading end portion of the second tubularmember is joined to an outer periphery of the first tubular member. Aportion that forms the double pipe portion of the second tubular membercomprises a first portion located closer to an end of the first tubularmember, and a second portion that is located closer to an end of thesecond tubular member and that has an enlarged diameter compared withthe first portion. A resonance chamber is formed between the firsttubular member and the second portion. A communication path that allowscommunication between the exhaust flow path and the resonance chamber isformed between the first tubular member and the first portion. AHelmholtz type resonant system is formed by the resonance chamber andthe communication path.

According to such a configuration, exhaust noise can be reduced in aconnection between the first tubular member and the second tubularmember. Furthermore, the Helmholtz type resonant system can be formedwith a simple structure because the resonance chamber and thecommunication path of the Helmholtz type resonant system are formedusing the double pipe portion formed by the two tubular members thatform the exhaust flow path.

In the above-described configuration, a spacer that inhibits contactbetween the first tubular member and the second tubular member may beprovided in the communication path, and the spacer may be arranged so asto secure an air passage on an outer circumference of the first tubularmember so that the communication path is not blocked. According to sucha configuration, the communication path is less likely to be blocked,and an effect of reducing exhaust noise can thereby be enhanced.

Furthermore, in the above-described configuration, each of the firsttubular member and the second tubular member may be formed as a singlepart. According to such a configuration, it is not necessary toseparately use dedicated components to form the Helmholtz type resonantsystem, and thus, space saving, cost reduction, and the like can besought.

It is to be noted that one aspect of the present invention can beachieved in various forms, such as an exhaust system including amuffler, and a method for muffling exhaust noise, besides theabove-described muffler.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an exhaust system of an embodiment.

FIG. 2 is a sectional view taken along a line II-II in FIG. 1.

FIG. 3A is an exploded perspective view of a muffler, and FIG. 3B is atransparent perspective view of the muffler.

FIG. 4 is a sectional view taken along a line IV-IV in FIG. 2.

EXPLANATION OF REFERENCE NUMERALS

1 . . . exhaust system, 2 . . . flow path member, 3 . . . catalyticconverter, 4 . . . sub-muffler, 5 . . . main muffler, 10 . . . firsttubular member, 11 . . . reduced diameter portion, 12 . . . bodyportion, 20 . . . second tubular member, 21 . . . enlarged diameterportion, 22 . . . body portion, 23 . . . leading end portion, 30 . . .muffler, 31 . . . resonance chamber, 32 . . . communication path, 40 . .. wire mesh

MODE FOR CARRYING OUT THE INVENTION

An embodiment in which the present invention is applied will bedescribed below with reference to drawings.

An exhaust system 1 shown in FIG. 1 forms an exhaust flow path, which isa flow path of exhaust gas discharged from an internal combustion engineof an automobile. The exhaust system 1 is mainly configured with a flowpath member 2 of a tubular shape forming the exhaust flow path having along actual length. The exhaust system 1 has a catalytic converter 3, asub-muffler 4, and a main muffler 5 arranged in series with each otherin order from the upstream of the exhaust flow path (from the left inFIG. 1) along the flow path member 2 (the exhaust flow path).

The flow path member 2 comprises a first tubular member 10 that formsthe exhaust flow path in the downstream of the sub-muffler 4, and asecond tubular member 20 that is connected to a downstream-side endportion of the first tubular member 10 and forms the exhaust flow pathin the upstream of the main muffler 5. In the flow path member 2, thesub-muffler 4 and the main muffler 5 are connected to each other via thefirst tubular member 10 and the second tubular member 20.

As shown in FIG. 2, FIG. 3A, and FIG. 3B, the first tubular member 10 isa member formed by processing a circular pipe part having an outsidediameter R1 (60.5 mm, for example), and is configured as a single part.Specifically, the first tubular member 10 is a member formed by reducingin diameter an end portion located in the downstream side (the rightside in FIG. 2) of the circular pipe part having the outside diameterR1, specifically a portion having a length L1 from an end, to an outsidediameter R2 (54.7 mm, for example) that is smaller than the outsidediameter R1. In an explanation below, the portion having the length L1from the end of the first tubular member 10 is referred to as a “reduceddiameter portion 11”, and the remaining portion is referred to as a“body portion 12”.

The second tubular member 20 is a member formed by processing thecircular pipe part having the outside diameter R1 similarly to the firsttubular member 10, and is configured as a single part similarly to thefirst tubular member 10. Specifically, the second tubular member 20 is amember formed by enlarging in diameter an end portion located in theupstream side (the left side in FIG. 2) of the circular pipe part havingthe outside diameter R1, specifically a portion having a length L2 froman end, to an outside diameter larger than the outside diameter R1.Specifically, the second tubular member 20 is gradually increased inoutside diameter from a position the length L2 apart from the end towardthe end, and becomes largest in outside diameter (120 mm, for example)at a position a length L3 apart from the end (L3<L2). Then, the secondtubular member 20 is gradually decreased in outside diameter from aposition a length L4 apart from the end (L4<L3) toward the end. Such ashape is formed by performing a diameter enlarging process on theportion having the length L2 from the end and then performing a diameterreducing process on a portion having the length L4 from the end, forexample. In an explanation below, the portion having the length L2 fromthe end in the second tubular member 20 is referred to as an “enlargeddiameter portion 21”, and the remaining portion is referred to as a“body portion 22”.

The downstream-side end portion of the first tubular member 10,specifically the entirety of the reduced diameter portion 11 and part ofthe body portion 12, is inserted into the second tubular member 20 froman upstream-side end portion (a leading end portion 23 of the enlargeddiameter portion 21) of the second tubular member 20 in such a mannerthat central axes thereof are coincident with each other. In this way, adouble pipe portion including the first tubular member 10 as an innerpipe and the second tubular member 20 as an outer pipe (a portion inwhich the first tubular member 10 and the second tubular member 20overlap with each other) is formed in a connection (a joint to bedescribed later and a portion adjacent thereto) between the firsttubular member 10 and the second tubular member 20. The connectionbetween the first tubular member 10 and the second tubular member 20functions as a muffler 30 of a Helmholtz type resonant system, as willbe described below.

That is, the second tubular member 20, specifically the leading endportion 23 of the enlarged diameter portion 21, is joined (welded allaround in the present embodiment) to the first tubular member 10,specifically on an outer periphery of the body portion 12. In this way,in the double pipe portion, a dead-end space is formed that communicateswith the exhaust flow path, between the first tubular member 10 and thesecond tubular member 20. Specifically, a resonance chamber 31 having alarge volume is formed between the body portion 12 of the first tubularmember 10 and the enlarged diameter portion 21 of the second tubularmember 20. In other words, a volume required as the resonance chamber 31is secured by the enlarged diameter portion 21 of the second tubularmember 20. Besides, a communication path 32 is formed between thereduced diameter portion 11 of the first tubular member 10 and the bodyportion 22 of the second tubular member 20. The communication path 32 isa space a cross-sectional area of which orthogonal to an axial directionis smaller than that of the resonance chamber 31, and allowscommunication between the exhaust flow path and the resonance chamber31. The resonance chamber 31 and the communication path 32 are designedto configure the Helmholtz type resonant system.

Provided in the communication path 32 is a wire mesh 40, which is ametal buffer member. The wire mesh 40 functions as a spacer to inhibitcontact between the first tubular member 10 and the second tubularmember 20. Moreover, the wire mesh 40 also has a function of reducingstress of thermal contraction difference between the first tubularmember 10 and the second tubular member 20. It is to be noted that anoutside diameter of the wire mesh 40 is equal to or smaller than theoutside diameter R1 of the body portion 12 of the first tubular member10.

However, if the communication path 32 is blocked by the wire mesh 40,excitation force of sound pressure that generates a resonance phenomenonbecomes less likely to be transmitted to the resonance chamber 31. Thus,the wire mesh 40 is arranged so that an air passage is secured in anouter circumference of the first tubular member 10. Specifically, in thepresent embodiment, a plurality of (three in this example) the wiremeshes 40 having a circular arc shape along the outer periphery of thefirst tubular member 10 are arranged on some parts of the entire outercircumference (range of 360 degrees) of the first tubular member 10, asshown in FIG. 4. The three wire meshes 40 are not as long as the entireouter circumference of the first tubular member 10 even when all of themare pieced together. Besides, the three wire meshes 40 are arrangedshifted from each other in an axial direction of the first tubularmember 10 (on different positions in the axial direction) (see FIG. 2).Consequently, the air passage is secured successfully on the outercircumference of the first tubular member 10.

The muffler 30 is designed such that a resonance frequency thereof iscoincident with an Nth-order mode (N is a natural number, and 1 in thepresent embodiment) of air column resonance frequency of a pipe, and theend of the first tubular member 10 is arranged so as to be at a positionof the maximum sound pressure of the Nth mode.

According to the embodiment described above in detail, the followingeffects are obtained.

[A1] The muffler 30 comprises the first tubular member 10 that forms theexhaust flow path of the internal combustion engine, and the secondtubular member 20 that is connected to the first tubular member 10 andforms the exhaust flow path together with the first tubular member 10.In the connection between the first tubular member 10 and the secondtubular member 20, the double pipe portion is formed in which the end ofthe first tubular member 10 is inserted into the second tubular member20 from the leading end portion 23 thereof, and the leading end portion23 of the second tubular member 20 is joined to the outer periphery ofthe first tubular member 10. The portion that forms the double pipeportion of the second tubular member 20 comprises the body portion 22located closer to the end of the first tubular member 10, and theenlarged diameter portion 21 that is located closer to the end of thesecond tubular member 20 and that has the enlarged diameter comparedwith the body portion 22. The resonance chamber 31 is formed between thefirst tubular member 10 and the enlarged diameter portion 21. Thecommunication path 32 that allows communication between the exhaust flowpath and the resonance chamber 31 is formed between the first tubularmember 10 and the body portion 22. The Helmholtz type resonant system isformed by the resonance chamber 31 and the communication path 32.

Thus, according to the present embodiment, air column resonance can beinhibited at the connection between the first tubular member 10 and thesecond tubular member 20, and as a result, exhaust noise can be reduced.Moreover, the Helmholtz type resonant system can be configured with asimple structure because the resonance chamber 31 and the communicationpath 32 of the Helmholtz type resonant system are formed using thedouble pipe portion formed by the first tubular member 10 and the secondtubular member 20 that form the exhaust flow path. Especially, since theHelmholtz type resonant system is adopted, a muffling effect can beenhanced by increasing the volume of the resonance chamber 31. Althoughit may be possible to create a through-hole in the first tubular member10 and to cause the through-hole to function as the communication pathof the Helmholtz type resonant system, sufficient effect is less likelyto be obtained by such a structure because the length of thecommunication path is no more than the through-thickness of the firsttubular member 10. In this regard, the structure having the longcommunication path is achieved in the present embodiment, and noisereduction effect can thereby be enhanced.

[A2] The wire mesh 40 that inhibits contact between the first tubularmember 10 and the second tubular member 20 is provided in thecommunication path 32. The wire mesh 40 is arranged so as to secure theair passage on the outer circumference of the first tubular member 10 sothat the communication path 32 is not blocked. Thus, according to thepresent embodiment, the communication path 32 is less likely to beblocked, and an effect of reducing exhaust noise can thereby beenhanced.

[A3] Each of the first tubular member 10 and the second tubular member20 is formed as a single part. Thus, according to the presentembodiment, it is not necessary to separately use dedicated componentsto form the Helmholtz type resonant system, and thus, space saving, costreduction, and the like can be sought. Specifically, in a configurationin which dedicated components to form a muffler (a resonance chamber anda communication path) are added to the components forming the exhaustflow path, the structure is likely to be complicated and larger, and thenumber of the components is increased as well as the number of portionsto be joined (welded), which is likely to result in increase in cost. Incontrast, the muffler 30 of the present embodiment is configured withthe first tubular member 10 and the second tubular member 20 forming theexhaust flow path and, furthermore, the number of the portions to bejoined (welded) is one. Thus, the muffler 30 of the present embodimenthas an advantage that space saving, cost reduction, and the like can beeasily sought. In addition, since the muffler 30 of the presentembodiment is configured with the tubular members, there is anotheradvantage that the muffler 30 has a bending workability and can beeasily applied to a layout of the exhaust system 1.

[A4] The muffler 30 is designed such that the resonance frequencythereof is coincident with the Nth-order mode of the air columnresonance frequency of the pipe, and the end of the first tubular member10 is arranged so as to be at the position of the maximum sound pressureof the Nth mode. Thus, according to the present embodiment, the maximumreduction can be obtained with the mode coincident with the resonancefrequency. Furthermore, the air column resonance can be inhibited byreducing the sound pressure by a certain volume even in the other mode.

[A5] The first tubular member 10 has the reduced diameter portion 11formed therein, and the wire mesh 40 having the outside diameter equalto or smaller than the outside diameter R1 of the body portion 12 isused. Thus, the first tubular member 10 having the wire mesh 40 attachedthereon can be easily inserted into the second tubular member 20.Consequently, according to the present embodiment, the first tubularmember 10 and the second tubular member 20 can be assembled to eachother more easily.

Although the embodiment of the present invention has been describedabove, it is needless to say that the present invention is not limitedto the above embodiment and can take various forms.

[B1] The wire mesh 40 shown in the above embodiment is an example, andthe configuration is not limited to this. For example, the wire mesh 40may be one in number or may be two or more in number. The position inwhich the wire mesh 40 is arranged is also not limited in particular.Specifically, two C-shaped wire meshes having a shape of a halved ring,for example, may be arranged shifted in the axial direction of the firsttubular member 10. Moreover, a member other than the wire mesh 40 may beused as the spacer. Furthermore, the spacer may be formed by processing(for example, by forming projecting portions on) at least one of thefirst tubular member 10 and the second tubular member 20. Alternatively,a configuration without the spacer may be possible.

[B2] The first tubular member 10 may be formed of a plurality of parts.For example, when a circular pipe part having the outside diameter R2and a circular pipe part having the outside diameter R1 are used, anarea to be reduced in diameter can be decreased, or the diameterreducing process itself can be eliminated. Similarly, the second tubularmember 20 may also be formed of a plurality of parts.

[B3] The first tubular member 10 may comprise no reduced diameterportion 11. For example, it may be possible to insert the first tubularmember 10 on which the wire mesh 40 is attached into the second tubularmember 20, and then, to reduce the diameter of the leading end portion23 of the second tubular member 20.

[B4] In the above embodiment, the first tubular member 10 and the secondtubular member 20 are formed using the circular pipe parts having thesame outside diameter. However, the configuration is not limited tothis. For example, a circular pipe part having an outside diameterlarger than that of the first tubular member 10 may be used as thesecond tubular member 20. Moreover, the first tubular member 10 and thesecond tubular member 20 may be formed using parts other than thecircular pipe part (a tubular member having a section of oval orpolygonal shape, for example).

[B5] The resonance chamber 31 shown in the above embodiment is anexample, and the configuration is not limited to this. For example,although the resonance chamber 31 is formed by the enlarged diameterportion 21 that is expanded into an approximately trapezoidal shape whenviewed from the side (viewed from a direction orthogonal to the axialdirection) in the above embodiment, the resonance chamber, instead ofthis, may be formed by an enlarged diameter portion expanded into, forexample, an approximately triangular shape or an approximatelyrectangular shape.

[B6] In the above embodiment, the configuration has been exemplified inwhich the muffler 30 is arranged in the exhaust flow path connecting thesub-muffler 4 and the main muffler 5 to each other. However, theconfiguration is not limited to this. Moreover, the configuration of theexhaust system on which the present invention is premised is also notlimited to the above embodiment, and a configuration without asub-muffler may be adopted, for example. Furthermore, a positionalrelationship between the first tubular member (an inner pipe of thedouble pipe portion) and the second tubular member (an outer pipe of thedouble pipe portion), i.e., whether they are located upstream ordownstream, may be opposite to that in the above embodiment. That is,the second tubular member may be arranged in the upstream of the exhaustflow path, and the first tubular member may be arranged in thedownstream of the exhaust flow path.

[B7] Each of the elements of the present invention is a conceptual one,and is not limited to the above embodiment. For example, the function ofone element may be dispersed over a plurality of elements, or thefunctions of a plurality of elements may be integrated to one element.Moreover, at least part of the configuration of the above embodiment maybe replaced by a known configuration having a similar function.

1. A muffler comprising: a first tubular member that forms an exhaustflow path of an internal combustion engine; and a second tubular memberthat is connected to the first tubular member and forms the exhaust flowpath together with the first tubular member, wherein a double pipeportion is formed in which an end portion of the first tubular member isinserted into the second tubular member from an end portion thereof,wherein a leading end portion of the second tubular member is joined toan outer periphery of the first tubular member, wherein a portion thatforms the double pipe portion of the second tubular member comprises afirst portion located closer to an end of the first tubular member, anda second portion that is located closer to an end of the second tubularmember and that has an enlarged diameter compared with the firstportion, wherein a resonance chamber is formed between the first tubularmember and the second portion, wherein a communication path that allowscommunication between the exhaust flow path and the resonance chamber isformed between the first tubular member and the first portion, andwherein a Helmholtz type resonant system is formed by the resonancechamber and the communication path.
 2. The muffler according to claim 1,wherein a spacer that inhibits contact between the first tubular memberand the second tubular member is provided in the communication path, andwherein the spacer is arranged so as to secure an air passage on anouter circumference of the first tubular member so that thecommunication path is not blocked.
 3. The muffler according to claim 1,wherein each of the first tubular member and the second tubular memberis formed as a single part.
 4. The muffler according to claim 1, whereinthe second tubular member is connected to an end portion in thedownstream side of the first tubular member.
 5. The muffler according toclaim 4, wherein the first tubular member is a member comprising areduced diameter portion, which is a portion formed by reducing indiameter a portion having a specified length from a downstream-side endof a circular pipe part, and a body portion, which is anon-reduced-diameter portion, wherein the second tubular member is amember comprising an enlarged diameter portion, which is a portionformed by enlarging in diameter a portion having a specified length froman upstream-side end of a circular pipe part, and a body portion, whichis a non-enlarged-diameter portion, wherein a downstream-side endportion including an entirety of the reduced diameter portion and partof the body portion of the first tubular member is inserted into thesecond tubular member, wherein the resonance chamber, which is adead-end space that communicates with the exhaust flow path, is formedbetween the body portion of the first tubular member and the enlargeddiameter portion of the second tubular member, and wherein thecommunication path is formed between the reduced diameter portion of thefirst tubular member and the body portion of the second tubular member,the communication path being a space, a cross-sectional area of whichorthogonal to an axial direction is smaller than that of the resonancechamber and which allows communication between the exhaust flow path andthe resonance chamber.
 6. The muffler according to claim 1, wherein thesecond portion is shaped such that the second portion is graduallyincreased in outside diameter from a position a length L2 apart from theend toward the end, becomes largest in outside diameter at a position alength L3 apart from the end (L3<L2), and is gradually decreased inoutside diameter from a position a length L4 apart from the end (L4<L3)toward the end.